linux-kernel - Re: [PATCH 0/6] genirq/test: Platform/architecture fixes

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Message-ID: <2143e074-c82f-4f38-84c7-6a39c6c6ecd3@roeck-us.net>
Date: Fri, 22 Aug 2025 11:34:04 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Brian Norris <briannorris@...omium.org>
Cc: Thomas Gleixner <tglx@...utronix.de>, David Gow <davidgow@...gle.com>,
 linux-kernel@...r.kernel.org, kunit-dev@...glegroups.com
Subject: Re: [PATCH 0/6] genirq/test: Platform/architecture fixes

On 8/21/25 12:06, Brian Norris wrote:
> On Thu, Aug 21, 2025 at 10:02:52AM -0700, Guenter Roeck wrote:
>> Build results:
>> 	total: 162 pass: 162 fail: 0
>> Qemu test results:
>> 	total: 637 pass: 637 fail: 0
>> Unit test results:
>> 	pass: 640616 fail: 13
>> Failed unit tests:
>> 	arm64:imx8mp-evk:irq_cpuhotplug_test
>> 	arm64:imx8mp-evk:irq_test_cases
>> 	m68k:q800:irq_test_cases
>> 	m68k:virt:irq_test_cases
>>
>> Individual failures:
>>
>> [   32.613761]     # irq_cpuhotplug_test: EXPECTATION FAILED at kernel/irq/irq_test.c:210
>> [   32.613761]     Expected remove_cpu(1) == 0, but
>> [   32.613761]         remove_cpu(1) == -16 (0xfffffffffffffff0)
>> [   32.621522]     # irq_cpuhotplug_test: EXPECTATION FAILED at kernel/irq/irq_test.c:212
>> [   32.621522]     Expected add_cpu(1) == 0, but
>> [   32.621522]         add_cpu(1) == 1 (0x1)
>> [   32.630930]     # irq_cpuhotplug_test: pass:0 fail:1 skip:0 total:1
> 
> I managed to get an imx8mp-evk setup running (both little and big
> endian) and couldn't reproduce. But I'm guessing based on the logs that
> we're racing with pci_call_probe(), which disables CPU hotplug
> (cpu_hotplug_disable()) for its duration.
> 
> I'm not sure how to handle that.
> 
> 1. I could just SKIP the test on EBUSY. But that'd make for flaky test
>     coverage.
> 2. Expose some method to block cpu_hotplug_disable() users temporarily.
> 3. Stop trying to do CPU hotplug in a unit test. (It's bordering on
>     "integration test"; but it's still useful IMO...)
> 4. Add an EBUSY retry loop? Or some other similar polling (if we had,
>     say, a cpu_hotplug_disabled() API).
> 

Here is an additional data point: It only happens with big endian tests.
This always happens in my setup, and it only happens when booting from
virtio-pci but not when booting from other devices.

I just re-ran the test and it passed this time, so this is apparently
a flake. I'd suggest to ignore it for now. If I see it again and find
a clean way to reproduce it we can have another look. The emulated PCIe
controller for imx8mp-evk isn't exactly stable, so this may just be a side
effect of emulation problems.

Guenter